I honestly believe that the water temp has more to do with gender determination (and egg survival of a certain gender) than anything.

If fish are like humans, more males will be born to a well-fed female. Typically female infant mammals can survive more stressful conditions than males; this is why most premature babies who survive are female. I don't know how applicable this is to fish, but if it's down to sex chromosomes then it could be true across species. I have heard of first time breeders often getting all female spawns, so that does lend credence to the theory :)